We have obtained well-labeled monkey fetuses using intravenous injections of 3Hthymidine (3HT) into the pregnant female on a known day of gestation. Retinal sections have been successfully double labeled for cell birth date (3HT autoradiography) and cell markers (immunocytochemistry). Currently three series are being collected at Fd45, Fd55 and Fd72 with 4-5 fetuses in each series. This material will provide an invaluable resource for the analysis of retinal growth and for determining the sequence of cell generation and differentiation within subpopulations of retinal neurons. An analysis of double-labeled dopamine amacrine cells has shown that these large cells are born somewhere in the middle of the amacrine types. They are never heavily labeled for 3HT, which would show that they are the first to be generated; the first amacrine cells to be generated are large amacrines, which contain the neurotransmitter GABA. However, dopamine amacrines are significantly m ore labeled than other amacrines, putting them in the middle of the cascade of amacrine generation. FUNDING NIH grants RR00166, EY04536, EY07031 and EY01730, and by a Kayser Award. Hendrickson, A., Sears, S., and Bumsted, K. Expression of photoreceptor-specific proteins in primate retina. Med. Sci. Monitor 4 11-16, 1998. Bumsted, K. and Hendrickson, A. Distribution and development of short-wavelength cones differ between Macaca monkey and human fovea. J. Comp. Neurol. 403 502-516, 1999.